Congenital sucrase-isomaltase deficiency (CSID) is a chronic, autosomal recessive, inherited, phenotypically heterogenous disease with variable enzyme activity. CSID is usually characterized by a subject having complete or almost complete lack of endogenous human sucrase activity, along with a very marked reduction in isomaltase activity, a moderate decrease in maltase activity, and the subject can have normal or abnormal lactase levels.
The human enzyme sucrase-isomaltase is naturally produced in the brush border of the small intestine, primarily the distal duodenum and jejunum. The natural human enzyme hydrolyzes the disaccharide sucrose into its component monosaccharides, glucose and fructose. Isomaltase breaks down disaccharides from starch into simple sugars.
In the absence of endogenous human sucrase-isomaltase enzyme, as in CSID, sucrose is not metabolized. Unhydrolyzed sucrose and starch are not absorbed from the intestine and their presence in the intestinal lumen leads to osmotic retention of water. This may result in loose stools or diarrhea. Unabsorbed sucrose in the colon is fermented by bacterial flora to produce increased amounts of hydrogen, methane and water. As a consequence, excessive gas, bloating, abdominal cramps, nausea, vomiting, and explosive diarrhea may occur. Chronic malabsorption of disaccharides may result in malnutrition. Undiagnosed/untreated CSID patients often fail to thrive and fall behind in their expected growth and development curves. Prior to the FDA approval of the commercial replacement product Sucraid® (sacrosidase) Oral Solution, the treatment of CSID has required the continued use of a strict sucrose-free diet with limited success in disease management.
CSID is currently treated by the oral administration, with meals, of a glycerol-water (1:1 w/w) solution of sacrosidase, which provides the enzyme replacement therapy for CSID. This solution is commercially provided as Sucraid® (sacrosidase) Oral Solution distributed by QOL Medical LLC. Each milliliter (mL) of Sucraid® contains 8500 International Units (I.U.) of the enzyme sacrosidase, the active ingredient. The chemical name of this enzyme is β,D-fructofuranoside fructohydrolase. The enzyme is derived from baker's yeast (Saccharomyces cerevisiae), by enzymatic digestion with papain.
The Sucraid® product was typical of the era with respect to purity. The FDA established purity specification was not less than 85% in the main band(s) by reduced SDS-PAGE densitometry analysis following Coomassie staining. This is a band ratio of sacrosidase to other proteins of about 6:1.
The purity was specified by the FDA to comprise not more than 10 μg/mL of papain in the sacrosidase drug substance. The “drug substance” is the precursor glycerol:water solution of sacrosidase that can be further diluted and packaged to yield Sucraid®, which is referred to as the finished “drug product.” The original label approved by FDA in 1998 made notice of potential for allergic reactions, and cautioned doctors to treat CSID patients for the first time within their unit in case allergic reactions arose. Again, in 2008, as the result of a site change of the drug substance manufacturer, the FDA only approved the re-launch of this drug with the imposition of a Risk Evaluation and Mitigation Strategy (REMS) which are only required by the FDA for drugs with the potential for serious safety problems.
It has been reported that the primary structure of sacrosidase consists of 513 amino acids with an apparent molecular weight of 100,000 g/mole for the glycosolated monomer (range 60,000-116,000 g/mole). Reports also suggest that the protein exists in solution as a monomer, dimer, tetramer, and octomer ranging from 100,000 g/mole to 800,000 g/mole. It has an isoelectric point of 4.1 (pI=4.093).
Presently, Sucraid® is provided in bottles containing 118 mL of the sacrosidase solution. A typical dose is either 1 or 2 mL with every meal or snack. The solution is bottled aseptically; however, it may become contaminated after opening due to the necessity of frequent administration, so patients are instructed to discard the bottle 4 weeks after opening.